Blowout preventer

ABSTRACT

An annular blowout preventer comprising a housing having a bore through it and an annular recess extending outwardly from the bore, and a packer within the recess including an annulus of deformable material having a bore aligned with the housing bore and a circular series of rigid inserts extending therethrough from one end to the other. A sealing surface on an end portion of the annulus engages the oppositely facing end surface of the recess, and there are radially movable parts about the outer side of the annulus for constricting the packer to urge its bore into position to seal about a member in the bore of the housing or upon itself when the bore is empty. The packer is symmetrical end-for-end so that it may be disposed with either end up, and each of the rigid inserts includes a rib having a flange at each end. The flanges are skewed in the unconstricted position of the annulus and are caused to swing into more radial positions as the annulus is constricted. The sides of the flanges are adjacent one another to confine the annulus at its opposite ends and cause the inserts to move in unison, and the radially innermost ends of the flanges are substantially adjacent the bore of the annulus when unconstricted, so as to be moved into a position within the bore of the preventer housing as the annulus is constricted.

United States Patent [72} Inventors Marvin R. Jones; Primary Examiner-William F. ODea Benton Baugh, Houston, Tex. Assistant Examiner-Richard Gerard 21] Appl. No. 765,061 Anrneyl-lyer, Eickenroht, Thompson & Turner [22] Filed Oct. 4,1968 [45] Patented Mar. 30, 1971 I i ['73] Assignee Cameron Iron Works, Inc. ABSTRACT: An annular blowout preventer comprising a Houston. Tex. housing having a bore through it and an annular recess extending outwardly from the bore, and a packer within the recess including an annulus of deformable material having a bore aligned with the housing bore and a circular series of rigid inserts extending therethrough from one end to the other. A [54] BLOWOUT PREVENTER sealing surface on an end portion of the annulus engages the 17 Claims 11 Drawing Figs oppositely facing end surface of the recess, and there are radially movable parts about the outer side of the annulus for con- [52] US. Cl 251/ l, stricting the packer to urge its bore into position to seal about 277/235 a member in the bore of the housing or upon itself when the [51] Int. Cl E2lb 33/06 bore is empty. The packer is symmetrical end-for-end so that [50] Field of Search 25 1/14, 5. 7. i may b di d with either end up, and each of the rigid in- 2 1 3 5 1 v serts includes a rib having a flange at each end. The flanges are 185, 235 skewed in the unconstricted position of the annulus and are caused to swing into more radial positions as the annulus is [56] References constricted. The sides of the flanges are adjacent one another UNITED STATES PATENTS to confine the annulus at its opposite ends and cause the inl,708,261 4/1929 Crowell et al 166/86 serts to move in unison, and the radially innermost ends of the 2,609,836 9/1952 Knox 277/73 flanges are substantially adjacent the bore of the annulus when 2,846,178 8/1958 Minor.... 251/1 unconstricted, so as to be moved into a position within the 3,323,773 6/1967 Walker l /l bore of the preventer housing as the annulus is constricted.

Patented March so, 1971 3,572,627

".5 Sheets-Sheet l 27 I ,fa; I K Z e4 25 64 l Z Mafwn R. (/4309: flex? fan F. Bqugfi INVEN'IORS ATTO/PA/E VJ Patented March 30, 1971 3,572,627

5 Sheets-Sheet 2 IN VEN'I 'ORS z A TI'OR/VE VJ Mar w P. zfone: .Ben for? f Bauyfi Patented March 30, 1971 5 Sheets-Sheet 3 Mar W0 A. Jon 6*: .Benfan ff .Bauyfi INVLiN'TORS ATTOR/VEKS Pate ntecl March 30, 1971 5 Sheets-Sheet 4 Patented March so, 1971 3,572,627

5 Sheets-Sheet 5 ATTORNEVJ BLOWOUT PREVENTER This invention relates generally to blowout preventers and, more particularly, to improvements in annular blowout preventers.

As well known in the art, a blowout preventer controls the pressure within an oil or gas well during drilling and completion of the well. It comprises a housing adapted to be connected above the head of the well with its bore aligned with the well bore, and one or more packing elements carried within a recess in the bore. The packing element or elements are adapted to be moved inwardly for closing about a pipe or other member in the bore or for closing the entire bore when it is empty.

An annular blowout preventer has a single packer comprising an annulus of rubber whose bore is adapted to be radially constricted. In one such annular blowout preventer, shown and described in U.S. Pat. No. 2,609,836, the packer comprises a massive annulus of rubber having rigid inserts molded into it for containing it during construction. These inserts extend from one end to the other of the annulus and comprise longitudinally extending ribs having flanges at their opposite ends which move radially inwardly as the bore is constricted.

The flanges are arranged radially of the annulus and the sides of adjacent flanges are spaced apart so that they may move inwardly as the annulus is constricted. The radially in nerrnost ends of the flanges are disposed substantially adjacent the bore of the annulus in the unconstricted position of the annulus, so that as the annulus is constricted, these ends will move into the bore of the preventer housing. Thus, even though the bore of the annulus moves inwardly beyond the inner ends of the flanges, the latter overhang a sufficient portion of the annulus to prevent its being blown out by well pressure.

Obviously, however, as the packer is used to close off on itself, or even on small objects in the bore of the preventer housing, a greater amount of overhang may be required. With the preventer shown in the aforementioned patent, this could be accomplished only by reducing the diameter of the housing bore or by extending the inner ends of the flanges into the housing bore, which would reduce the effective or useful diameter therethrough when the packer is unconstricted. The operating conditions for which the preventer is designed do not normally permit this.

Also, since there are spaces between the sides of the flanges, the portions of the annulus beneath these spaces must be recessed. Otherwise, the annulus would be extruded into the spaces and thereby either cause the extruded rubber to be pinched off or prevent full and uniform inward movement of the inserts.

An object of this invention is to provide an annular preventer and a packer therefor in which the overhang is increased without a reduction in the effective housing bore in the unconstricted position of the packer.

Another object is to provide an annular blowout preventer and a packer therefor in which the effective radial extent of each of the flanges or other platelike insert parts at opposite ends of the packer increases as the annulus is constricted.

A further object is to provide such a preventer in which the ends of the annulus are confined against extrusion between such parts and in which the inserts as a whole are caused to move in unison upon constriction of the annulus.

These and other objects are accomplished, in accordance with the illustrated embodiment of the present invention, by an annular blowout preventer in which the plates of a substantially circular series of rigid plates on at least one end of the packer annulus have their radially innennost ends substantially adjacent the bore of the annulus and are skewed with respect to such bore when the annulus is unconstricted. As a result, the plates swing into more radial positions, as the annulus is constricted, to increase their effective radial extents. Thus, the plates are caused to overhang the annulus to a greater extent than heretofore possible with annular preventcrs having conventional packers with radially disposed insert flanges of the type above described.

More particularly, the sides of the plates are wedge-shaped in plan and adjacent one another to confine the annulus against extrusion between them and to cause them to move in unison as the annulus is constricted. In the illustrated embodiment of the invention, the plates are arranged at both ends of the annulus so that the packer may be arranged in the preventer housing with either end up. Preferably, ribs extend through the annulus in circularly spaced-apart relation, and each is connected to a plate at each end which overhangs the rib to form a flange. This controls to some extent the flow of the resilient annulus material and minimizes the tendency for the overhanging ends of the plates to bend under pressure.

In the drawings, wherein like reference characters are used to designate like parts;

FIG. I is a perspective view of an annular blowout preventer constructed in accordance with the present invention, as seen from the top and side thereof, and with a portion removed to show a pipe within the bore of the packer in its unconstricted position;

FIG. 2 is a vertical sectional view through the blowout preventer of FIG. I, as seen along broken line 2-2 of FIG. I;

FIG. 2A is a partial top plan view of the packer of the preventer of FIGS. 1 and 2, as seen along line 2A-2A of FIG. 2, with the packer in its unconstricted position and showing in broken lines the ribs of itsri'gid inserts;

FIG. 3 is a vertical sectional view through a portion of the packer, upon an enlarged scale and as seen along broken line 3-3 of FIG. 2A;

FIG. 4 is a cross-sectional view, on an enlarged scale and as seen along broken line 4-4 of FIG. 2, of a connection between adjacent packer constricting parts which synchronizes their radial movement;

FIG. 5 is a partial vertical sectional view of the preventer, similar to FIG. 2, but showing the packer upon constriction inwardly to seal about the pipe in the bore of the housing;

FIG. 5A is a top plan view of the packer, as seen along line 5A-5A of FIG. 5 and similar to FIG. 2A, but with the packer in the constricted position of FIG. 5;

FIG. 6 is another partial sectional view similar to FIG. 5, but showing the packer in a further constricted position to close an open hole in the bore of the preventer housing;

FIG. 6A is a top plan view of the packer, as seen along line 6A-6A of FIG. 6, but with the packer in the constricted position of FIG. 6;

FIG. 7 is a perspective view of a rigid insert; and

FIG. 8 is a horizontal sectional view of the insert, as seen along broken line 8-8 of FIG. 7.

With reference now to the details of the above described drawings, the preventer, which isdesignated in its entirety by reference character 20, includes a housing 21 which is annular in shape and has a cylindrical bore 22 extending axially through it. Threaded holes 23 and ring grooves 24 are provided at both ends of the housing for coaxial connection and sealing to other wellhead members (not shown).

With the preventer 20 thus connected as a part of the wellhead, a drill pipe P forming part of the drill string may extend through its bore 22 and into the well bore. Alternatively, a Kelly or other out-of-round member may extend through the bore 22 of the blowout preventer. Still further, the bore may be empty so as to form an open hole" therethrough. As known in this art, there may be occasion for the preventer to be used in sealing about the member in the hole, such as the pipe P or the Kelly, so as to close off the annular space between such member and the bore 22, or alternatively to seal off with itself so as to close an open hole.

Housing 21 is made up of a body 25 which is generally L- shaped in vertical, half cross section to provide an upwardly opening shelf about its interior, and a cap 26 disposable over the upper end of the body 25 to form an annular recess 27 about bore 22. Cap 26 has a bore 22a therethrough which forms a continuation of a bore 22b through the lower end of body 25, the two bores thus forming the bore 22 through the housing. Body 25 includes a bridging ring 40 (to be described below), and cap 26 and the top surface of the ring form the upper and lower ends 27a, and 27b, respectively, of the recess. The outer wall of recess 27 is concentric with bore 22 of the housing, and the ends 270, and 27b of the recess are perpendicular to its axis.

Cap 26 is secured to the upper end of the body by a series of cap screws 28 extending through holes in the cap for connection with threaded holes 29 in the body 25. Threaded holes 30 in cap 26 may receive eyes for lifting it into and out of place. An O-ring 31 about a reduced lower end portion of the cap seals with respect to an inner annular wall 32 of the body 25 above the recess 27.

A packer 33 is disposed within the recess 27 of the preventer housing 21 for movement between an unconstricted position in which its bore 35 is substantially axially aligned with the housing bore 22, as best shown in FIGS. 1 and 2, and a constricted position in which its bore 35 is moved radially inwardly into the housing bore for sealing about the pipe P, as best shown in FIG. 5, or for sealing upon itself when the bore is empty, as best shown in FIG. 6. As will be described in detail below, the packer is so moved by means of constricting parts including laterally extending segments 36 disposed about the outer side of the packer within recess 27 and adapted to be moved radially inwardly and outwardly by means of the hydraulically operated pistons.

Packer 33 is cylindrical in shape, with its outer side and bore 35 concentric, and its ends 37 and 38 perpendicular to the axis of the bore 35. It fits closely within the upper and lower ends 27a and 27b of the recess and, as best shown in FIG. 2, when the packer is unconstricted, segments 36 are disposed with their inner arcuate faces adjacent its outer side and their outer arcuate faces adjacent the outer side of the recess 27. Bore 22b of the housing is connected to the radially outer portion of the recess 27 behind the outer side of the packer by a series of slots 39 formed in a bridging ring 40 to pennit well pressure to act over the outer side of the packer.

The constricting segments 36 are circumferentially spaced to permit them to move radially inwardly to constrict the packer. As will be apparent from FIG. 4, they are caused to move in unison by means of pins60 connecting the opposite ends of adjacent segments. Thus, one end of each pin is threadedly received in a socket 61 in one segment, while its other end is slidably received in a socket 62 in an adjacent segment. Each segment is so moved by means of a piston 63 having a seal ring 69 slidable within a cylinder 64 extending inwardly from the outer side of body 25 of housing 21. Each piston is connnected to a segment 36 by a rod 66 having a stud 65 threadedly connected between a socket on the innner end of the rod and a central hole in the segment. Each rod 66 extends through a seal such as an O-ring 67 carried within an opening 68 through the housing 25 between the recess 27 and a cylinder 64.

Upon removal of the cap 26 from the body 25 of the housing, the packer 33 may be lifted from or lowered into the recess 27. With the packer removed from the recess, access may be had to the segments 36 for replacing or repairing them. Thus, the threaded connection of each stud 65 to the piston rod enables the rod to be disconnected from the stud, so that the segment may be withdrawn and removed from its operating position within the recess 27 The outer ends of cylinders 64 are closed by means of a ring 70 which surrounds body 25 and is seated on a shoulder 71. This ring is normally prevented from moving upwardly by a pin 70a removably connected to cap 26. However, when the pin is removed, the ring may be lifted from and lowered into position for closing the cylinders 64. When lifted, the ring 70 permits access to any one or all of the pistons 63 for replacing or repairing them. Due to the threaded connection of the piston rod 66 to the stud 65, the piston may be rotated so as to release it from the stud 65 and permit it to be withdrawn from its cylinder 64.

Seal rings 72 and 73 about body 25 above and below cylinders 64 seal with respect to ring 70 to form an annular space about pistons 63 into which pressure fluid may be introduced through a conduit 74 connecting with a passageway 75 leading thereto. This pressure fluid urges the pistons inwardly and thus the packer to a constricted position.

Alternatively, pressure fluid may be introduced into cylinders 64 on the inner side of pistons 63 to urge them outwardly and permit the packer to expand. This fluid is introduced through a conduit 75a, connecting with an annular passageway 76 which is formed from the lower side of the body 25 and then covered by a ring 77 welded to the body. Individual passageways 78 then connect passageway 76 with the inner end of each cylinder 64.

Packer 33 includes a massive annulus 34 of rubberlike material having its bore 35 formed therethrough and a circular series of rigid inserts 41 which extend through the annulus from one end to the other. Each such insert is bonded to the annulus and includes a rib 42 having a flange 43 at each end which overhangs the rib on all sides, as best shown in FIGS. 7 and 8. The ribs are disposed generally midway between the bore 35 and the outer side of the annulus, while the flanges are disposed with their radially innermost ends 43a, flush with the bore when the annulus is unconstricted.

The radially outermost ends 43b, of the flanges 43 are disposed inwardly of the outer side of the annulus to leave an annular portion at each end of the annulus surrounding the flanges. As best shown in FIG. 3, each annular portion protrudes at 44 beyond the adjacent end surface of the flange 43 for engaging the opposite end surface of recess 27. Inward movement of the segments 36 constricts the packer, urging the top protuberance upwardly against the upper end of the recess to supplement the action of well pressure on the lower end of the packer.

Although the protruding surfaces on the lower end of the annulus may also fonn a seal against the lower end 27b, of the recess, the lower portion 22b, of the bore is nevertheless connected through slots 39 to the recess behind the annulus. Thus, well pressure will still have access to the recess 27 behind the outer wall of the annulus. Since the protruding surface on the upper end of the annulus seals with respect to the upper end 27a, of the recess, the differential between this well pressure and atmospheric pressure in the upper portion 22a of the bore is effective over a substantial portion of the height of the packer to supplement the force of the actuators of the segments 36 in maintaining the annulus in its constricted position.

Inasmuch as the packer is symmetrical end-for-end, it may be disposed in the recess 27 of the housing with either end up. Thus, if an upper protruding surface is damaged, the packer may be inverted to dispose the effective lip at its upper end.

As the packer is constricted, the rigid inserts 41 are also caused to move inwardly, although to a lesser extent than the annulus itself. That is, as will be appreciated from a comparison of FIGS. 1 and 2 with FIGS. 5 and 6, upon constriction of the packer, the vertically midportion of its bore 35 will move radially inwardly past the innermost ends 43a, of the flanges 43 of the inserts. As the rigid inserts move inwardly, these innermost ends move into the bore 22 of the housing to overhang a portion of the annulus which has moved into the bore 22, thereby reducing the likelihood of extrusion of the annulus past the flanges.

As shown in FIG. 2A, when the packer is unconstricted, the flanges 43 are skewed with respect to the bore of the packer. Thus, the axis of each flange-Le, a plane bisecting the flange from end to end--extends at an acute angle with respect to a radius of the packer which passes through the centroid of the flange. Since constriction of the annulus causes its inner portions to move radially inwardly at a greater rate than the outer portions thereof, and the rigid inserts 41 are bonded to the annulus, the flangeswill swing to a more radial orientation with respect to the packer bore. Thus, as can be seen from the drawings, the flanges swing from the skewed positions of FIG. 2A, when the packer is unconstricted, to a more radial position when the packer is constricted to seal about a pipe, as shown in FIG. 5A, and to a still more radial position when the packer is constricted to seal upon itself, as shown in FIG. 6A.

Thus, the effective radial extent of each flangei.e., the radial distance between the radially innermost and outermost ends 43a and 43b thereof-increases during constriction of the packer. This is in contrast to the behavior of initially radially disposed flanges, as in the packers of the above mentioned patent, which have the same effective radial extent at all degrees of constriction of the packer. As a result, the rigid inserts of the packer of the present invention occupy less initial space for a given amount of subsequent overhang.

As in the packer of the previously mentioned patent, the rubber forming the annulus is free to flow between the circularly spaced-apart ribs 42 as the packer is constricted. However, as distinguished from the prior packer, the sides of the flanges 43 of adjacent inserts 41 engage one another in both the unconstricted and constricted positions of the annulus. Thus, as previously described, the rubber at opposite ends of the annulus is confined against extrusion between the flanges. Also no one flange at an end of the annulus is free to move relatively to the remainder, so that in fact all the flanges and thus the inserts move in unison.

The opposite sides of the rib 42 of each insert are parallel to one another and also arranged with the vertical plane bisecting each rib disposed at an acute angle to the radius of the annulus passing through the centroid of the rib. More particularly, the opposite sides of rib 42 are disposed approximately within planes of least strain of the rubber of the annulus during movement of the annulus from unconstricted to constricted positions, so as to reduce the likelihood of breaking the bond between the ribs and the annulus, with consequent reduction of its effective life.

These planes of least strain may extend at acute angles on either side of the radius. However, in the case of the inserts 4, which swing as a whole toward more radial positions during constriction of the annulus, it is preferred that the sides of the rib be so disposed as to also be swung to more radial positions as the annulus is constricted. In this way, the ribs do not detract from the tendency of the inserts 41 to twist as a whole toward their more radial positions.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombina- -tions are of utility and may be employed with reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. A packer for use in an annular blowout preventer, comprising an annulus of deformable material having a bore therethrough, and a substantially circular series of rigid plates which are responsive to movement of said material and which are arranged on at least one end of the annulus with their end surfaces generally perpendicular to the bore and their radially innermost ends substantially adjacent the bore, when the annulus is unconstricted, to cause their effective radial lengths to increase as the annulus is constricted and said end surfaces to move radially inwardly of the bore along a path generally perpendicular thereto.

2. A packer of the character defined in claim 1, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.

3. A packer for use in an annular blowout preventer, comprising an annulus of deformable material having a bore therethrough, and a substantially circular series of rigid plates on at least one end of the annulus, the radially innermost ends of the plates being substantially adjacent the bore, when the annulus is unconstricted, and the plates being responsive to movement of said material and arranged with their end sur-.

faces generally pe endic ular to the bore so as to swim from skewed to more ra rally disposed positions w1th respect 0 said bore as the annulus is constricted.

4. A packer of the character defined in claim 3, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.

5. A packer of the character defined in claim 3, wherein the sides of the plates converge toward the bore of the annulus.

6. A packer of the character defined in claim 5, wherein the sides of the plates are adjacent one another to confine the annulus and cause the plates to swing in unison.

7. A packer of the character defined in claim 6, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.

8. A packer for use in an annular blowout preventer, comprising an annulus of deformable material, and a substantially circular series of rigid plates on at least one end of the annulus, the radially innermost ends of the plates being substantially adjacent the bore of the annulus, when the annulus is unconstricted, and a plane bisecting each plate extending at an acute angle with respect to a radius of the annulus which extends through the centroid of the plate, when the annulus is unconstricted, said plate being responsive to movement of said material so that, as said annulus is constricted, said bisecting plane is swung toward said radius to reduce the acute angle therebetween to thereby increase the effective radial extent of each plate.

9. A packer of the character defined in claim 8, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.

10. A packer of the character defined in claim 8, wherein the sides of the plates converge toward the bore of the annulus.

11. A packer of the character defined in claim 10, wherein each side of each plate engages a side of an adjacent plate so as to confine the annulus and prevent any one plate from moving independently of the remainder during constriction of the packer.

12. A packer of the character defined in claim 11, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.

13. An annular blowout preventer, comprising a housing having a bore therethrough and an annular recess in the bore, and a packer comprising an annulus of resilient material within the recess and having a bore therethrough substantially aligned with the bore of the housing, when the annulus is unconstricted, and a substantially circular series of rigid plates on at least one end of the annulus having end surfaces slidable over an adjacent end surface of the annular recess in the housing, said adjacent surfaces of the plates and recess being generally transverse to the aligned bores of the housing and annulus, and said plates being responsive to movement of said material so as to cause the radially innermost ends of the plates to move inwardly into the bore of the housing and increase in effective radial lengths as the annulus is constricted.

14. An annular blowout preventer of the character defined in claim 13, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.

15. An annular blowout preventer of the character defined in claim 13, wherein the plates are arranged to swing from skewed to more radially disposed positions with respect to the bore as the annulus is restricted.

16. An annular blowout preventer of the character defined in claim 15, wherein the sides of the plates are adjacent one another to confine the annulus and cause the plates to swing in unison.

17. An annular blowout preventer of the character defined in claim 16, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates. 

1. A packer for use in an annular blowout preventer, comprising an annulus of deformable material having a bore therethrough, and a substantially circular series of rigid plates which are responsive to movement of said material and which are arranged on at least one end of the annulus with their end surfaces generally perpendicular to the bore and their radially innermost ends substantially adjacent the bore, when the annulus is unconstricted, to cause their effective radial lengths to increase as the annulus is constricted and said end surfaces to move radially inwardly of the bore along a path generally perpendicular thereto.
 2. A packer of the character defined in claim 1, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.
 3. A packer for use in an annular blowout preventer, comprising an annulus of deformable material having a bore therethrough, and a substantially circular series of rigid plates on at least one end of the annulus, the radially innermost ends of the plates being substantially adjacent the bore, when the annulus is unconstricted, and the plates being responsive to movement of said material and arranged with their end surfaces generally perpendicular to the bore so as to swing from skewed to more radially disposed positions with respect to said bore as the annulus is constricted.
 4. A packer of the character defined in claim 3, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.
 5. A packer of the character defined in claim 3, wherein the sides of the plates converge toward the bore of the annulus.
 6. A packer of the character defined in claim 5, wherein the sides of the plates are adjacent one another to confine the annulus and cause the plates to swing in unison.
 7. A packer of the character defined in claim 6, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.
 8. A packer for use in an annular blowout preventer, comprising an annulus of deformable material, and a substantially circular series of rigid plates on at least one end of the annulus, the radially innermost ends of the plates being substantially adjacent the bore of the annulus, when the annulus is unconstricted, and a plane bisecting each plate extending at an acute angle with respect to a radius of the annulus which extends through the centroid of the plate, when the annulus is unconstricted, said plate being responsive to movement of said material so that, as said annulus is constricted, said bisecting plane is swung toward said radius to reduce the acute angle therebetween to thereby increase the effective radial extent of each plate.
 9. A packer of the character defined in claim 8, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.
 10. A packer of the character defined in claim 8, wherein the sides of the plates converge toward the bore of the annulus.
 11. A packer of the character defined in claim 10, wherein each side of each plate engages a side of an adjacent plate so as to confine the annulus and prevent any one plate from moving independently of the remainder during constriction of the packer.
 12. A packer of the character defined in claim 11, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.
 13. An annular blowout preventer, comprising a housing having a bore therethrough and an annular recess in the bore, and a packer comprising an annulus of resilient material within the recess and having a bore therethrough substantially aligned with the bore of the housing, when the annulus is unconstricted, and a substantially circular series of rigid plates on at least one end of the annulus having end surfaces slidable over an adjacent end surface of the annular recess in the housing, said adjacent surfaces of the plates and recess being generally transverse to the aligned bores of the housing and annulus, and said plates being responsive to movement of said material so as to cause the radially innermost ends of the plates to move inwardly into the bore of the housing and increase in effective radial lengths as the annulus is constricted.
 14. An annular blowout preventer of the character defined in claim 13, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates.
 15. An annular blowout preventer of the character defined in claim 13, wherein the plates are arranged to swing from skewed to more radially disposed positions with respect to the bore as the annulus is restricted.
 16. An annular blowout preventer of the character defined in claim 15, wherein the sides of the plates are adjacent one another to confine the annulus and cause the plates to swing in unison.
 17. An annular blowout preventer of the character defined in claim 16, wherein the plates are arranged on each end of the annulus and ribs extend through the annulus each to connect a pair of plates. 